This invention relates to chemical conversion materials for aluminum and aluminum alloys and in particular the invention relates to a thixotropic chemical conversion material.
Chemical conversion materials are applied to aluminum and aluminum alloys to react therewith to form a corrosion resistant coating thereon and to provide a surface for improved bonding of organic finishes such as paints and lacquers which may be applied to the coating.
A currently used conversion material is formulated from chromates, inorganic salts such as phosphates or fluorides, catalysts, activators and accelerators. Although this material reacts with aluminum to form an adequate corrosion resistant coating it has several drawbacks. When the material is prepared in an aqueous solution its consistency is too thin for proper spray application, i.e., rapid run off occurs. The material does not always produce a uniform coating of sufficient thickness for maximum corrosion protection. The material cannot be applied to vertical and curved surfaces without rapid run off which produces uneven discontinuous coatings of varying thickness resulting in ineffective corrosion protection and paint adhesion as well as waste of material.